This invention relates to the control of pests, and more particularly, to an apparatus and method for controlling and eliminating rodents, particularly rats, from a prescribed area. The most pertinent prior art U.S. Pat. Nos. are: 3,636,559, 2,922,999.
It has long been known that rodents, and particularly rats, are adversely affected by high frequency sound waves which are generally beyond the audible frequency spectrum of human beings and domestic animals. In particular, rodents are adversely affected by sound waves extending from 18 KHz. It has also been found that sound waves generated from square wave signals are even more irritating to rodents. It should be understood that square wave signals are defined to include what may be more aptly described as rectangular shaped periodic signals, as well as square shaped periodic signals. Furthermore, it is extremely difficult to generate waves which have square corners so that waves which are substantially square should also be considered as falling within the definition of square wave signals.
It has been discovered that rats which were trained to easily traverse a maze became disoriented and could not traverse the maze when subjected to ultrasonic sound waves. This phenomina occurred at sound levels of 2 to 5 db. A decrease in the reproduction rate of rats continuously exposed to ultrasonic sound waves has also been noted. It has been theorized that the ultrasonic sound waves are in nearly the same frequency range as the communication sounds made by the rats so that the ultrasonic sound waves disrupt their communications. As communication between the rats plays an important role in their reproduction ritual, a disruption of communication due to the generated ultrasonic sound waves results in reduction in the reproduction rate.
An ultrasonic sound wave of any frequency within the range of 18 to 30 KHz, at a sufficient intensity or loudness, will be extremely irritating to a rodent, causing the rodent to do almost anything, including on occasion self-destruction, to escape the sound; however, if the rodent does not escape from the area in which the ultrasonic sound wave is present, and is not destroyed, it will develop a deafness immunity to the sound wave which is known as the "slotted hearing syndrome". The rodent will lose this deafness immunity if generation of the ultrasonic sound wave is discontinued for a period of time so that the rodent will have to redevelop the deafness immunity upon resumption of the generation of the ultrasonic sound wave. The rodent's deafness immunity is confined to the particular frequency of ultrasonic sound wave to which it is subjected so that a slight variation of the frequency being generated, after immunity has developed, will again irritate the rodent.
Several different devices have been manufactured for controlling rodents. Although the manufacturers of these devices may not have been aware of the deafness immunity characteristic of rodents, they were aware of the fact that the generation of ultrasonic sound waves which vary in frequency and duration was far more irritating to rodents than the generation of an ultrasonic sound wave frequency. Consequently, the devices previously manufactured generated ultrasonic sound waves which varied in a number of ways in order to irritate the rodents. Certain devices produced ultrasonic sound waves which continuously varied in frequency from 20 KHz to 30 KHz then back to 20 KHz. Others varied the frequency as noted and also varied the intensity or amplitude of the sound waves generated. Still other devices interrupted the cyclically varying ultrasonic sound wave frequencies at varying interruption rates. None of these devices, however, recognized and utilized the facts that (a) rodents are most irritated by some particular frequencies within the ultrasonic frequency range and (b) that the variation over the ultrasonic frequency range of the sound waves produced need be for only a relatively short period of time in order to prevent the rodent from developing a deafness immunity. The recognition and utilization of these characteristics comprise the heart of this invention. The implementation of these characteristics via the method and apparatus described in this application results in the generation of ultrasonic sound waves which are most irritating and devastating to rodents.